Silicided shallow p+n junctions have been formed by implanting BF2+ ions into a-Si/Co bilayer films on Si substrates and subsequent drive-in/silicidation. The effects of implantation dose and energy on the electrical characteristics were studied. The modulation ranges of implantation energy and dose employed to form good junctions are large for the present fabrication scheme. However, high-performance silicided shallow junctions must be optimized by using moderate implant energy and dosage. The junction depth, drive-in efficiency, dopant concentration and electrical characteristics must be compromised to achieve the goal of good shallow junctions. A silicided shallow junction formed by the implantation of 70 keV at a dose of 5 × 1015 cm-2 and subsequently annealed at 700°C exhibited characteristics with a leakage current density lower than 0.5 nA cm-2, a forward ideality factor better than 1.01 and a junction depth of about 0.13 μm.